Conventionally, high pressure air (compressed air) obtained by compression in an air compression device is used for driving a device such as a vehicle brake device or a door opening/closing device. FIG. 1 and FIG. 4 of Japanese Unexamined Patent Publication No. H11-201039 (hereinafter, called as Patent Literature 1) discloses an air compression device to be loaded in a railway vehicle. In the air compression device illustrated in FIG. 4 of Patent Literature 1, the air which is brought to a high temperature state by compression in a compressor is cooled by an after cooler (a cooler). The cooled compressed air is dehumidified in a dehumidifier. The dehumidified compressed air is stored in an air tank. The compressed air stored in the air tank is supplied to the aforementioned device.
The following problem may occur when a rotary compressor such as a scroll compressor is used as a compressor in the aforementioned conventional air compression device. Specifically, compressed air remains between the compressor and the dehumidifier after the scroll compressor is stopped. As a result, when the scroll compressor is stopped, the remaining compressed air flows back toward the compressor, and may rotate a scroll (a rotary piston) in the backward direction. The number of backward rotations may gradually increase, and may reach as high as about 3,000 rpm. Sound generated in this case may vary, as the rotation number changes. Therefore, it is necessary to prevent generation of such abnormal sound. Further, when the number of backward rotations exceeds an allowable rotation speed of the compressor, the durability of the scroll may be adversely affected.
In order to prevent the drawbacks resulting from backflow as described above, there is proposed an idea of providing a check valve at a position near the compressor on the discharge side of the compressor. For instance, in the air compression device disclosed in Patent Literature 1, a check valve is provided on the suction side of the compressor. It is possible to provide a check valve in a discharge flow channel of a compressor, specifically, in a flow channel between the compressor and the after cooler. However, the temperature of the air to be discharged from the compressor may reach as high as around 200° C. Therefore, when a check valve is provided as described above, it is necessary to use an expensive high temperature oriented member such as a seal member for the check valve. Thus, there is room for improvement regarding the maintenance cost.
Further, in the air compression device illustrated in FIG. 1 of Patent Literature 1, a check valve is disposed in a suction flow channel connected to a suction port of the compressor as described above. However, the suction flow channel is in a low pressure state. Therefore, even if a check valve is provided in the suction flow channel, backflow of compressed air in a high temperature state cannot be completely prevented. Thus, it is difficult to completely prevent backflow of compressed air toward the compressor.